It has been proposed to manufacture parabolic antennas with reinforced plastics for their primary merits of superior resistance to corrosion and light weight, replacing conventional metal-made antennas which are manufactured by press and other metal processings made with aluminum, steel or other metals. Manufacture of antennas with reinforced plastics involves processes where a material for an electric conductive reflector (hereinafter abbreviated as a reflector), such as metal net, or carbonfiber mat, is piled with other reinforcing and/or resineous materials, and is molded into an intended parabolic shape as a whole. However, undesirable problems involved therein are such that the reflector is not accurately configured to adequately define an exact geometrical parabola, because of uneven internal pressures occurring in the molding process in a mold. Further, partial breaks of the reflector material are liable to take place. In principle, a reflector is embedded or enclosed in reinforcing resineous materials and hardened during the manufacture where a built-in reflector should take an exact parabolic configuration to achieve superior focussing of waves toward the focus point of the antenna surface. Therefore, dislocation thereof from predetermined positions in a mold during the hardening of resineous materials including the reflector or possible breaks due to extreme uneven molding pressure should be prevented. Further re-adjustment of reflector position after molding is almost impossible to be effected, therefore it is an important task to develop a technique for molding without fear of dislocation, much less breaking of the reflector surface.